Airfoil, and particularly helicopter blade



R. MAYN E March 11, 1952 AIRFOIL., AND PARTICULARLY HELICOPTER BLADE snventor Foer May/1e Gttomeg March 11, 1952 R, MAYNE 2,589,193

AIRFOIL, AND PARTICULARLY HELICOPTER BLADE Filed NOV. 29, 1946 2 SHEETS-SHEET 2 mventor W l Cttorneg Patented Mar. 11, 1952 AIRFOIL, AND PARTICULARLY HELICOPTER BLADE Robert Mayne, Akron, Ohio, assignor to Goodyear Aircraft Corporation, Akron, Ohio, a corporation of Delaware Application November` 29, 1946, Serial No. 713,157

8 Claims. 1

This invention relates to airfoils, and, more particularly, to helicopter blades or other rotary airfoils, and is concerned specifically with the construction of such airfoils.

Heretofore, airfoils of various types have been proposed and used, in both the stationary and rotary airfoil elds. Strength, Weight, balance, and eiiiciency problems arise, and it is well recognized that many improvements can be made in existing structures. But particularly in rotary airfoil the need for improvement has been recognized. Present rotary airfoils are largely of the type employing wood and fabric components, but it is believed that these are responsible for much of the vibration and poor performance of present day helicopters. Accurate mass, aerodynamic balance, and precision of contour are not possible with atmospherically unstable materials. In addition, abrasion and aerodynamic loads and the high operating velocities encountered in a helicopter blade produce serious wear and distortion of the fabric covering. In rotary airfoils the bending and centrifugal stresses are different and more complicated than in either xed wing airfoils or propellers. Cyclic pitch control occasioned by the rotary airfoil moving rst into the wind and thereafter with the wind when the helicopter is in forward flight complicate rotary airfoil design.

Without dwelling further upon the complications of airfoil and specifically rotary airfoil design, it is the general object of the application to avoid and overcome the difficulties of and objections to known airfoil designsby the provision of a relatively stable, and vibration-free airfoil having relatively high safety factors and relatively low weight.

Another object of the invention is to provide a rotary'airfoil of high performance characteristics including accurate mass, aerodynamic balance and precision of contour, and capable of being used over long periods and under a wide variety of temperatures with substantially no maintenance costs.

Another object of the invention is the provision of an airfoil having a considerable portion 4thereof made of stainless steel and including features of monocoque construction.

Another object of the invention is to provide arotary airfoil with built in deicing means.

Another object of the invention is the provision of an airfoil including laminated skins covering at least a part of the airfoil, and with means for joining the laminated skins together at the trailing edge of the airfoil.

Another object of the invention is to provide .an airfoil, and particularly a rotary airfoil having substantially the forward third of the airfoil formed from a unitary integral piece of sheet metal of monocoque construction.

" The foregoing lobjects of the invention, and

other objects which will become apparent as the description proceeds, are achieved by the provision of an airfoil having a main spar, preferably of stainless steel, a unitary, high strength metal sheet, also ordinarily of stainless steel, formed to provide a monocoque structure for substantially the forward third of the airfoil, the rear edges of the metal sheet being secured to the spar, ribs extending rearwardly of the spar, and a plastic laminate having thin surface coverings of metal sheet, preferably stainless steel, secured to the top and bottom of the ribs and to the spar and acting as the skin for the remainder of the airfoil. The trailing edge of the airfoil preferably includes a wedge shaped, fabric reenforced plastic to which the trailing edges of the skins are adhesively secured. Preferably the monocoque structure of the leading edge of the airfoil provides a chamber for the passage of hot gases along the leading edge of the airfoil to prevent ice formation thereon, with the hot gases entering at the inner transverse end of the airfoil and exhausted through an opening in the tip of the airfoil.

For a better understanding of the invention reference should be had to the accompanying drawings, wherein:

Fig. 1 is a plan View of a helicopter blade incorporating the principles of the invention;

Fig. 2 is an enlarged vertical cross-sectional view taken substantially on line II-II of Fig. 1;

Fig. 3 is an enlarged vertical longitudinal sectional View taken substantially on line III-III of Fig. 1 and illustrating the manner of connecting the root spar to the blade;

Fig. 4 is a perspective view, partly broken away, of the helicopter blade incorporaiing the features of the invention;

Fig. 5 is a plan view of the airloil tip;

Fig. 6 is an enlarged view of the laminated skin on the airfoil, taken substantially on line VI-VI of Fig. 2; and

Fig. 'l is an enlarged cross-sectional view taken substantially on line VII-VII of Fig. 1, and illus- -trating the details of securing the trailing edges of the airfoil together.

Although the features of the invention may be employed in the construction of airfoils of various types, the invention is primarily concerned lwith rotary airfoils, and specifically helicopter blades, and accordingly, the invention has been so illustrated and will be so described. Referring to the drawings, the numeral l indicates generally a helicopter 'blade having a main or forward spar 2, an aft spar 3, rearwardly extending, laterally spaced ribs 4, a baille plate 5, a monocoque forward skin 6, a reenforcement l for the leading edge of the forward skin 6, a lead counter-weight 8, a heat exchanger iin 8a -held by the counter-weight, aft skins 9 and IU,

a trailing edge filler strip`| I, a tip l2, and a spar root I3.

For purposes of strength, and for other reasons which will be developed as the description proceeds, the main or forward spar 2 is made of stainless steel, and is of U-shape in cross-section, being provided with lightening holes I 4 along its forward vertical portion, in the manner best. seen in Fig. 4. The spar 2 is positioned on its side with the legs of the U extending rearwardly,

and the aft spar 3, also preferably made of stainless steel, and having lightening holes I5 therein, is received between the legs of the forward spar and is connected thereto. Baffie plate 5 is made of relatively light stainless steel, for example, .003 inch, and is secured over the front ofthe forward spar in the manner shown in Fig. 4. Of course, the forward spar is made of .a gauge of metal adapted to take the computed test loads with the required margin of safety, a typical gauge being in the neighborhood of .030 inch. The aft. spar 3 may be ofthe same gauge as the mainspar.

The forward skin 0 which is, as already noted, of monocoquefstructure having no internal support, ismade in a singleV unitary piece from stainlesssteel sheet, all in the manner described and claimed in. co-pending application, Serial No. 712,338, led November 26, 194e,` and entitled Method of Making Airfoils,r Helicopter Blades, Leading Edges, and the Like, which application matured into Patent No. 2,490,976 on December 13, 1949.`

The gauge of the stainless steel sheet forming the forward` skin Sissubstantially the same as that` employed in the main or forward spar 2, being in the neighborhood of .030. inch.

Oneimportant advantage in employing stainless steel for both the forward spar` 2 and the forward skin 6 is that these parts can bereadily andV effectively spotwelded together. Spotwelding of stainless steel is readily effected,it.being only necessary to watchvout `that too much. electrodepressure is not employed `so as,A to d avoid excessive dimpling-of the sheets inA the region of the vspot` weld, but` with th e spotl weldS 110ssessing high strength, and goodfatigue and, corrosion resistance characteristics., Similarly: the aft Spalt 3V is preferablyY spot welded iny position, aslgcanthe bailie plate 5. Also, the reenforcing member 'I for the leading edge; or, noseof the airfoil may be of stainless steel and canv be spot welded in position. Prior .to securing the, reenforcing member 1- into position, theI lead counter-weight 8 can be melted intoA thereenforcing` member, with the counter-weight 8- carrying the heat transfer n 8a. In order to lavoid unduly raising the temperaturel of the reenforcing strip 1, the counter-weight 8 is preferably made from a lead alloy having avrelativelyy low melting point.

It has been found advisable, in order to effect the best possible heat transfer relation between the n 8a, the counter-weight 8, and the leading edge of the forward skin 6, to secure the reenforcing member 'I to the inside of the leading edgeV ofr therforward skin by means other than spot welding. Specifically,A a plastic heatL conducting material, such as,a brazing, metalor solder, again flowablevat va relatively low ternperature, is preferably employed,

A few dimpled rivets, at rather widely sepa? rated longitudinally spaced points may be used to assist in fastening the forward skin to the 4 forward spar and the aft spar, in the manner best seen in Fig. 4.

The ribs 4 are preferably made of aluminum or aluminum alloy, and, as best seen in Fig. 4, are adapted to be secured by angle brackets I6 to the aft spar 3, at laterally spaced points along the aft spar, with the ribs 4 extending rearwardly of the airfoil. Ribs 4 are also connected to the legs of the forward spar, in the manner shown. The ribs are provided with lightening holes I'I, and with top and bottom flanges to which the aft skins 9 and I0 are adapted to be secured.

In order to prevent undesired flow of air longitudinally of the airfoil under the action vof, centrifugal force when the airfoil is being rotated in use, the, lightening holes I5 of the aft spar are closed by means of flexible air tight membranes which are adhesively secured over the lightening holes,and atV spaced ribs 4, for example, every other rib, the lightening holes Il are closed by similar membranes. Or at these spaced points ribs 4jrnay be used which do not include lightening holes.V This prevents sub-atmosphericV or super-atmospheric pressures in undesirable amounts from building up anywhere along the aftv portionof the airfoil during the rotation of the airfoil in use. The pressure differential between the inside and the outside of the aft skins shouldY never exceed a, maximum of approximately one-quarter pound per square inch, and this is achieved'in the present blade. Without the sectionalization described,v and with the air tending to flow out to the blade tip under centrifugal action, pressure differentials of -up to two pounds per square inch ormore may be obtained whichA is yhighly undesirable and which may effect changes in contour of the aft section of they airfoil. Each section of the airfoilv is vented to `the atmosphere, as will be understood. The forward. section of theairfoil does not have to be sectionalized becauseof the very considerable strength of the forward skin land forward spar.

Any moisture in the blade will be thrownby centrifugal force to the lower corner of thev rib and aft spar, due to thel lag angle of the blade, and al small hole is provided at that point in each ribrso that the water will ultimately reach the tipof theA airfoil from which it willv drain by the provision of a small hole suitably positioned lin the tip.

The aft skins 9 and I0 are-,made ,from a stainless, steel and plasticY laminate. Thisyis, because stainlesssteel sheet having a thickness of necessary strength, is too heavy. Aluminum oraluminum alloys lif employed as aft skins will have a different coefficient of expansion thanthe stainless steel spar and forward skin withtheresult that temperature changes would warp or distort .theblade. The invention employs, as best Seen in Fig. 6, a laminate structure having a center or filler I3 of. fabric reenforced thermo-setting plastic.v To the filler are secured on top vand bot.- tom very-thin sheets I9 and 20 of stainless steel. Preferably the, stainless steel sheets I9 and. 20 are secured to the ller plastic I8 by means of a thermo-setting cement, such as. manufactured under the trade-marks Pliobond or Cycleweld. Stainless steel sheets I9 and .20 are, as noted, ordinarily relatively thin, beingvin the neighborhoodof .0015 inch, with thel plastic fillerv having a thickness of about .007, the total thickness of thelaminate including the-adhesive being iny the-neighborhood Aof .018,inch, Theresult is a high strength, but relatively low Weight laminate skin which is capable of absorbing well within its mechanical strength, with usual safety factors, any forces to which the aft skins are subjected.

The aft skins 9 and I9 are riveted to the edges of the legs of the forward spar 2, and to the flanges of the ribs 4. Preferably a cushioning strip 2| of aluminum or aluminum alloy is secured by an adhesive, such as the thermo-setting cement heretofore described, to the inner surface of each aft skin 9 and IIJ adjacent the ribs 4. The strengthening strip 2I serves to provide extra strength for the laminate adjacent the ribs so that the skins 9 and IIJ can be riveted to the ribs and to the edges of the forward spar 2. All of the rivets used are countersunk into the laminate, and the stainless steel sheets I9 and 20 used in the laminate are preferably half hard so as to facilitate dimpling thereof without cracking. In order to strengthen the forward edge of the skins 9 and I9, filler strips 22 of aluminum or aluminum alloy-are adhesively secured thereto. Moreover, the filler strips 22 are of a thickness to build up the thickness of the laminate to a dimension equal to the gauge of the forward skin 6 so that the surface of the airfoil adjacent the line of butt engagement of the lforward skin 6 and the aft skins 9 and III will be flat and smooth.

The trailing edges of the aft skins 9 and I0 are lsecured to the wedge shaped trailing edge strip II by an adhesive cement. This is conveniently achieved, in the manners best seen in Figs. 4 and '7, by making the trailing edge strip II from a fabric reenforced thermo-setting plastic, and with the stainless steel sheet 20 on the inside of each of the skin laminates 9 and II) terminating short of the wedge shaped strip II. Thus, the plastic ller I8 of each laminate is positioned adjacent the wedge shaped strip II, and an adhesive cement, preferably one which is adapted to set without heat, for example that sold under the trade name Resin-X, is applied to the several parts which are clamped together until the cement dries. Rivets are not employed at the trailing edge because of the diiiicult angle and the small space in which they must be applied, and it has beenv found that the wedge shaped trailing edge strip II when assembled as de- --ably has forward to aft strengthening angles 23 secured-tothe inside of th top and bottom of the tip, andpillar brackets 24 extending between theI top and bottom surface of the tip. A steel counter-weight 25 secured to the tip extends into v'the end of the leading edge of the forward skin 6 and is secured thereto by blind rivets or other fastening means to secure the wing tip in position. Agusset plate 26 secured to the aft portion of the tip I2 functions to additionally anchor ,the tip in place. The tip is' formed with a hole 29, reenforced by an inside flange 30, the hole functioning-'as the discharge opening for hot gases entering through 'la nipple 3| at the inner end of the air-folland passed along inside the leading edge thereof.

.e .'As 'bestgseen VinFigs, I Zand 3, a spar root I3l ex- 'tends intotheiorwardspar 2.V The spar root I3 fis' of ya cross-sectional contour so that it will slide snugly, and in wedging relation inside of the forward spar 2 and the aft spar 3. Bolts 21 fasten the airfoil to the spar root in the manner best seen in Fig. 3. A fitting 28 is welded to the spar root I3, with the fitting being adapted to be secured in known manner to the rotary mechanism for the helicopter blade. The manner of making the spar. root I3 and the fitting 28 form the subject matter of a co-pending patent application, Serial No. 718,696, led December 27, 1946, and entitled Method of Making Spar Roots for Helicopter Blades and the Like, which application matured into Patent No. 2,485,534 on October 18, 1949.

From the foregoing it will be recognized that the various objects of the invention have been achieved by the provision of a relatively simple. high strength airfoil having many noteworthy features, and` particularly adapted for use as a helicopter blade. A novel monocoque structure for the forward section of the airfoil is provided, and the aft section of the airfoil is characterized by the use of a stainless steel laminate having lhigh strength and low weight. The airfoil has a built-in deicing chamber, centrifugally induced flow of trapped air in the blade is eliminated, and the airfoil is adapted to retain its shape and operating characteristics even when subjected to the complex and changing forces encountered in rotary airfoils, particularly helicopter blade operation.

While in accordance with the patent statutes one best known embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is .not to be limited thereto or therebyI the inventive scope being defined in the appended claims.

What is claimed is:

1. The combination in an airfoil of a main spar of stainless steel, a unitary, high strength stainless steel metal sheet formed to provide a .monocoque structureV for substantially the forward third of the airfoil and secured to the spar, ribs extending rearwardly of the spar, and a plastic laminate having a very thin surface covering of stainless steel secured to the ribs and to the spar and acting as the skin for the remainder of the airfoil, the total thickness of said laminate being smaller than the thickness of said unitary metal sheet. l

2. AThe -combination in an airfoil of al main spar, a unitary metal sheet formed to provide a monocoque structure for substantially the forward third of the airfoil and secured to the spar, ribs extending rearwardly of the spar, and a plastic laminate having a thin surface covering of metal sheet secured to the ribs and to the spar and acting as the skin for the remainder of the airfoil, the total thickness of said laminate being within the thickness of said unitary metal sheet.

3. In combination in an airfoil, a main spar positioned back from the leading edge about one third of the chord, a single piece of stainless steel sheet bent to form a monocoque substantially forwardl third of the airfoil, the edges of the 4sheet being secured to the spar, metal surfaced plastic laminates secured to the spar and extending rearwardly thereof to form the skin of the remainder of the airfoil, and internal bracing for the laminates, the total thickness of each of said laminates being within the thickness of said forward single sheet. 4. A helicopter rotor blade adaptedv to be heated with gases for deicing including a forward spar 'having `substantially a U-shape in cross-'sectionyanaft spar'also having a U.shape in cross-section beingnestedinithe forward spar, theflegs of both spars extending rearwardly and vthespar webs being spaced from each other to formabox-'like structure, -a spar root closely fitting --into and being secured to vvsaid structure for attachment tofarblade operating mechanism, an 'elongatedsheet or plate curved across itsxwidth to`form a leading-edge skin and having itsopposite edges .overlapping the respective legsrof the 'forward -spar so as to substantially vcover said-spar, -a baiile plate welded longitudinally to the front and the full length of the forward spar and forming-togetherwith theA leading edge skin a hot gas duct, aireinforcing plate running along the inside of and being spotwelded tothe leading edge skin, a central longitudinalheat transfer fin runited with `the reinforcing plate, a .counterweight'made of material having a low melting pointabeingcastinto. said reinforcing plate, ribs connectedto and .extending rearwardly'of the aft .spar and connected also to thelegs of the forward spar, bottomand top skinsextending from the leadingedgeiskinover the ribsto then-ailing wedge; each ofthe .bottom and top skinscornprisinga'laininate having surfaces cf thin stainless steel anda fibre-reinforced plastic llerof a total 'thicknessilessthanfthat of the l-eading edge skin, "a reinforced. plasticztrailingedge stripy of wedgeshape in cross-section to which the laminated -sknsv are adhesvely secured in. contact .withtheir plastic ller, an inlet for carrying hot vgases to said duct .at the rootendof the blade, Yand a blade-tip provided with an .opening communicatingfwithsaidhot gas ducttfor exhausting" heating gases carried therein.

5. A helicopter rotor blade including-a forward spar having substantially a U-shape in crosssection, an `aft spar also having a U-shape in cross-section being nested in the forward spar, the legs of both spar cross-sections extending rearwardly of the airfoil and the vertical webs of the spars being spaced from each other to form a box-like structure, an elongated sheet or plate curved across its width to form a leading edge skin and having its opposite-edges overlapping the respective legs of theforward spar so as to substantially cover said spar, ribs connected to and extending rearwardly of the aft spar andconnected valso to the legs of theforward spar, bottom and top skins extendingfrom the leading edge skin over the ribs to the trailing edge, each of the bottom andtop skins comprisingl a laminate having surfaces of thin stainless steel and a nbre-reinforced plastic filler, said laminate being of a total thickness notgreater than'. the thickness of the leading edge skin, and areinforced plastic trailing edge strip of wedgeshape in cross-section to which the laminated skins are adhesvely secured in contact with their plastic filler.

6. A helicopter rotor blade including a forward spar having substantially a U-shape in crosssection, an aft spar also having a U-shape in cross-section being nested in the forward spar, the legs of both spar cress-sections extending rearwardly of the airfoil and the vertical webs of the spars being spaced from eachother to form a box-like structure, an elongated sheet or plate curved across its width to forma leading edge skin and having its opposite edges overlapping the respective legs of the forward spar so as to substantially cover said'spar, ribs con* nested to and extending vrearwardly of the aft spar Vand connected also to the legsiof ,thef.f0r ward spaigand bottom and top skins extending from the leading edge skin over the ribs tozthe trailing edge, each of the bottom and top skins comprising a `laminate having surfaces Vof thin stainless steel and a fibre-reinforced plastic iiller, said laminate being of a total thickness not greater than ,thethickness of the leading edge skin.

7. Afhelicopter rotor bladeincluding a forward Vspar having substantially Ia U-shape in crosssection, .an .aft spar also having va U-shape `in crossfsection being nested inthe forwardspar, 4the legsfof both s par cross-sections extending rearwardly of the airfoil with the legs ofthe forward spar extending beyond the rear edge 4of the legs of the aft spar and the vertical websof-the Spars being spaced from each other to form a box-like structure, an Velongated sheet -or plate' curvedv across its Width to form a leading edge skin and having its Opposite edges overlapping the respective legs of the forward spar so as to substantially cover said spar, ribs connected ,to and-'extending rearwardly of the aft yspar and connected also to the legs ofthe forward spar, vand laminatedfbottom and top skins extending from `the rear edge of the leading edge skin over the ribs to the trailing edge and having stainless steel faces enclosing a reinforced core.v

8. The combination in a helicopter rotorbl'ade ci a leading edge skin consistingof a singlestainless steel sheet, skin members ,extendingrear- `wardly from said leading edge skin and forming therewith the surface of theairfoil, said skin members being formed of stainless steel lfaces including a fabric reinforced plastic core, a wedge-shaped fabric-reinforced plastic laminate positioned inside the trailing edge of the airfoil substantially the full length thereof, and selfcuring adhesive -securing the trailing edges vof the Yskin members to the wedge-shaped plastic laminate,` the inside steel of said skin members being shorterthantheir outer sheet to y.makethe wedge-shaped laminate contactthe plastic core VThe followingreferences are of recordin' the le of this patent:

UNITED STATES PATENTS Number Name Date 1,496,304 Dornier June', 1924 1,507,143 Towssaint SeptfZ, 1924 1,523,106 Dornier Jan. 13,1925 '682,202 Vaughn Aug. 2 8, 1928 1;864,438 Janson June"2l, 1932 1,874,685 'Wright Aug. l30, 1932 1,942,674 Whitsett Jann 9, 1934 1,976,480 'Carleton et al Oct.-9, 1934 1,988,085 VOrlando Jan. 15,' 1935 '2,164,678 VBennett July' 4, 1939 (2,189,785 Fahrney Feb. `1 3, 1940 2,341,997 Law et al. Feb. 15, 1944 '2;361`,438 .Turner '.Oct.'l 31; 1944 12,394,513 Chappedelaine Feb. 5,1946 .2,412,908 `vPlatt et. al. Dec.17, 1946 2,460,351 Hoffman-et al. Feb. 1,1949 2,469,480 Sikorsky 'May 10, 1949 `FOREIGN PATENTS Number Country Date f 417,139 GreatfBritain Sept-28,v l1934 `4:306,444 Great "Britain May l130, 41939 -807,110 'France Oct.*12,'1936 

